The present invention relates to valves, more particularly to weir valves.
A weir valve is a valve utilizing a resilient diaphragm to traverse a weir and prevent the flow of fluid over the weir. The diaphragm may be lifted off the weir, either hydraulically by the fluid when released or mechanically to permit flow over the weir.
Weir valves provide excellent sealing and isolation characteristics to effectively contain the fluid, substantially eliminating leakage or migration into the valve mechanisms or exterior of the valve. Weir valves are also more amenable than conventional valves in designing direct and streamlined fluid flow courses through the valves. In many applications, particularly in the semiconductor industry, quiescent or dead spots in the fluid flow course must be avoided as these can cause the fluid to become stagnant or degrade. Additionally, contaminants or suspended solids can accumulate in the quiescent or dead spots. Due to these advantages, weir valves are found in the biotechnological, pharmaceutical, chemical, semiconductor, food processing, beverage, cosmetic, and dairy industries.
The resilient nature of the diaphragm in weir valves presents difficulties in allowing small quantities of fluid flow. The resilient diaphragm creates a soft bottoming when the valve is seated, thus making it difficult to manually determine when and to what extent the valve is slightly unseated or open. Additionally, the closure position of the resilient diaphragm can be dependent upon the fluid pressure. For example, a weir valve which is not tightly closed can be opened by a slight pressure increase. Conversely, a weir valve that is slightly open under a given pressure can become closed when the fluid pressure drops. Further, in some situations, the resilient diaphragm will oscillate when the valve is throttled at low flow rates and high pressures resulting in downstream pressure oscillations. Pressure and flow rate fluctuations or oscillations are undesirable in virtually any application.
Many weir valves, particularly pneumatically operated ones, are simply not adjustable, having only an open or a closed position.
In many applications it is often desirable or necessary to allow limited quantities of the fluid to continue to flow after the particular application or use has ceased. For example, in the semiconductor manufacturing industry ionized water is often used in various processes. Such fluid is subject to degradation if the fluid flow in not continuous.
In many applications required flow rates can vary over a wide range, weir valves are not amenable to allowing or reliably controlling the relatively minute flow rates sometimes required. Additional fluid conduits and separate valves for supplying and controlling lower flow rates can result in the degradation, stagnation, and accumulation of contaminant type of problems in which weir valves are intended to prevent.